The FSF is not selling a product. There is no offer to buy or acceptance of that offer. In fact, **there is no product** To quote from the GPL:
Read it again: without even the implied warranty of MERCHANTABILITY. The FSF is being open that their code is not a salable product.
Anyone is welcome to come along and turn the FSF’s code into a salable product. They can do this by offering a warranty that the code has a useful purpose and can do so for whatever price they choose. Again to quote from the GPL:
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
The generally low price for GPLd software is a consequence of unfettered competition, something monopolists have a problem with.